Boise State’s main rushing threat is D.J. Harper, who has 10 touchdowns and 713 rushing yards this season.

At 5-foot-9, 205, the sixth year senior (he was granted an extra year of eligibility after season-ending knee surgeries in 2009 and 2010) is the shiftier of Boise State’s two backs.

Redshirt freshman Jay Ajayi is a 6-foot, 222-pounder who first saw action against BYU and has seen his role increase throughout the season.

“Jay is more of a bigger back, the kind that puts (his) pads down and goes,” said Broncos coach Chris Petersen. “It’s his first year playing for us, and we’re still trying to figure him out.”

The timeshare arrangement between the two is a little different from the one between SDSU’s Adam Muema and Walter Kazee, who generally get an equal number of carries – last week against UNLV they actually finished with 21 each.

Harper is still the Broncos’ main back, averaging about 18 carries a game to Ajayi’s eight.

Defensively it would appear that the matchup favors the Aztecs. Boise State’s defense is good against the run, but even better against the pass.

In contrast, the Aztecs’ forte this season has been stopping the run.

SDSU’s rush defense is 31st nationally, and the Aztecs have given up an average of 125 rush yards per game. They’ve also stuffed several of the nation’s leading rushers, including Nevada’s Stefphon Jefferson and Fresno State’s Robbie Rouse.

This will present a challenge for Harper and Ajayi.

On the flip side, pounding the rock might be the best way for SDSU to beat Boise State’s ferocious defense.

The Broncos (7-1 overall, 4-0 Mountain West) have given up next to nothing against the pass this year.

Boise State is No. 6 nationally in pass defense, and has allowed an average of 98 yards per game. Fresno State’s Derek Carr is the only quarterback who’s thrown a touchdown pass against the Broncos.

However, they’re giving up an average of 145 rushing yards a game, and SDSU has tasted success against Boise State on the ground.

In the Aztecs’ 52-35 defeat to the Broncos in 2011, Muema earned his first career start in place of an injured Ronnie Hillman and scored two rushing touchdowns while tallying 119 yards on 13 carries.

“It was his chance to finally step up, and he responded well,” said running backs coach Jeff Horton. “We talked about it today, how he should have great confidence knowing what he did a year ago.”

The Aztecs (6-3, 4-1) could use a big game from Muema, who disappeared against Nevada (47 yards on 13 carries) and got off to a rough start in the UNLV game, fumbling twice in the first half.

But Horton said those were aberrations, and that Muema isn’t playing any differently than he was earlier in the season, when he averaged 114 yards and a touchdown over the first four games.

“I don’t see any difference in him. He’s fine,” Horton said, adding that Nevada did a good job stopping the Aztecs’ run game, and pointing out that until UNLV, Muema had only fumbled once all year.

“Sometimes it happens,” Horton said. “The guys on TV who make 10 million dollars a year, they turn it over sometimes. We’re not immune to it.

“Adam had 143 yards last week. He’s very disappointed with the turnovers because part of our creed is that you can’t do that as a running back, and I know nobody feels worse about it than he does. But I’ve got all the faith and confidence in him.”

And if Muema can’t get it going against the Broncos, there’s always scrappy, persistent Kazee – the same guy who upended himself over the pile to score a goal line touchdown against UNLV last week.

“Walter Kazee and I just switch off when one gets tired, and it’s hard for defenses to adjust to that,” Muema said. “So it does a great job of throwing the defense off track.”